In a typical cellular radio system, wireless terminals, also known as mobile stations and/or User Equipments units (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals, hereinafter called UEs which is the same as User Equipments, can also be mobile telephones, i.e. “cellular” telephones, and laptops with wireless capability e.g., mobile termination, and thus are, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data via the RAN.
The RAN normally covers a geographical area which is divided into cell areas, also denoted cells, with each cell area being served by a base station e.g., a Radio Base Station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base station communicates over the air interface operating on radio frequencies with the UEs within range of the base stations.
In some versions, particularly earlier versions of the RAN, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The RNC, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to RNCs. In general, in LTE the functions of the RNC node are performed by the RBSs. As such, the RAN of an LTE system has an essentially “flat” architecture comprising RBSs without reporting to RNCs. In LTE networks the base station(s) is/are called eNodeB(s) or eNB(s).
3GPP is in the process of defining solutions for Minimizing Drive Tests (MDT). The intention of the Minimizing Drive Tests (MDT) work is documented in 3GPP TR 36.805 V9.0.0 (2009-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on Minimization of drive-tests in Next Generation Networks (Release 9).
Stage 2 of Minimizing Drive Tests (MDT) is currently being developed in TS 37.320, i.e., 3GPP TS 37.320, “Radio measurement collection for Minimization of Drive Tests (MDT); Overall description; Stage 2”. MDT Stage 2 includes a UE measurement logging function and immediate reporting function. The 3GPP TS 37.320 document essentially focuses on the UE measurement logging function.
An important use case for MDT is coverage optimization. For this purpose following UE measurements, or similar functionalities, are considered for UE-internal logging: Periodic, e.g. one every 5 s, downlink pilot signal strength measurements; a serving cell becomes worse than threshold; transmit power headroom becomes less than threshold; Paging Channel Failure i.e. Paging Control CHannel (PCCH) decode error; and Broadcast Channel failure.
The network can request the UE to perform logging of measurements. The UE executes measurements and logs these measurements internally in a sequential manner, containing, e.g., some hour of logged measurement information.
As described in FIG. 1, the UE indicates to the network if it has available log i.e. available logged measurements. The network node i.e. eNB/RNC determines if it should request the logged measurements or not. If it decides to do so then a request is sent to the UE to deliver the log in a report message. From the eNB/RNC, the reported logged measurements may further be sent to an OAM server or similar.
The current 3GPP assumptions on this log (i.e. logged measurements) feature are, e.g., as follows: the UE is required to maintain only one log at a time; one log only contains measurement information collected in one Radio Access Technology (RAT); a log can only be reported and indicated when the UE is in connected state; If UE is requested to start logging, e.g., by configuration, a possibly old log and configuration stored in UE is erased.
What the logged measurement report message in signal number 4 in FIG. 1 should look like has not yet been decided, as of the filing of this application. Some proposals for management of measurement report have been proffered.
As one example proposal for management of measurement reports, it has been suggested that a log i.e. logged measurements, are to be sent in a single packet, and keeping that single packet within the size limits of a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU). Keeping the single packet within the size limits of a PDCP PDU makes it possible to use a Radio Resource Control RRC message for reporting without being segmented into several smaller packets before being sent to the receiving node i.e., the eNB or NB/RNC in LTE or UMTS, respectively. One option of this proposal would be limiting the maximum size of a log in a UE to one RRC message that fits into one PDCP payload packet.
As another example proposal for management of measurement reports, it has been suggested to send a log i.e. a logged measurement that is larger than a RRC message with several RRC messages.
However, there are disadvantages to both example proposals mentioned above. For example, limiting the log size could prevent logging to complete for the whole configured run time i.e. logging duration, which can be several hours. The log could fill the limited log buffer in the UE before any measurement report has been possible to send to the network node. Before the configured logging duration time has ended, the UE would stop the logging so that to only allow the log size to be a single packet e.g. single RRC packet, and relevant measurements reports may not thereafter be logged. Also in the current MDT configuration a start time for the logging is not configurable. This means that for a prolonged logging campaign a long period between logging instances may be needed in the MDT configuration, alternatively new MDT configuration needs to be provided from the OAM periodically to be conveyed to MDT capable UEs.
For the other proposal, sending too many RRC packets in a row could, in poor radio environments or when handover would occur, create problems with the radio connections and could also create unnecessary radio link failures that will make the users suffer and logged data be lost.